Low-Loss Feedline on a Budget: Building 450 to 600 Ohm DIY Ladder Line from Common Materials

Low-Loss Feedline on a Budget: Building 450 to 600 Ohm DIY Ladder Line from Common Materials: A complete technical guide to DIY ladder line for amateur radio. Build 450–600 ohm open-wire feedline cheaply, with less loss than coax on any HF band.

VHF DXing Secrets: The Ultimate Guide to Tropospheric Ducting for Radio Hams

Ever heard signals travel hundreds or even thousands of kilometers beyond line-of-sight? That’s not magic—it’s tropospheric ducting.

This fascinating radio phenomenon happens when atmospheric conditions (like temperature inversions and high-pressure systems) bend and trap VHF/UHF signals, letting them travel far beyond their normal range.

For ham radio operators, this means unexpected DX contacts, strong distant signals, and sometimes even interference from stations you’d never normally hear.

If you’re into radio, propagation, or just curious how the atmosphere can act like a giant waveguide, this guide is worth your time:

🔗 https://vu3dxr.in/ultimate-guide-to-tropospheric-ducting-for-radio-hams/

27MHz AM Transmitter Circuit for hobbyists

Explore the classic 27MHz AM Transmitter circuit. Learn about its oscillator, modulation, and power stages to build your own radio projects.

The 27MHz frequency band has long been a favorite among electronics enthusiasts and amateur radio operators. This citizen’s band frequency offers excellent propagation characteristics and serves as an ideal starting point for understanding amplitude modulation (AM) transmission principles. Today, we’ll explore a well-designed 27MHz AM transmitter circuit that demonstrates classic RF engineering concepts while remaining accessible to hobbyists.

27MHz AM Transmitter Circuit for hobbyists: 

The Silent Revolution: DRM+ Radio in the FM Bands

The Silent Revolution: DRM+ Radio in the FM Bands: Discover how DRM Radio in FM Bands revolutionizing global broadcasting in 2026. From xHE-AAC technology to "Green Radio" movement..DRM+ Radio in the FM Bands

RF DIODE DETECTORS.

Simple diode detectors are not linear. There is a small forward voltage drop across the diode, and this voltage varies with diode current. Even if we allow for a fixed voltage drop across the diode, measurements will not be accurate at all power levels. At 1mA of diode current, the drop across a Schottky signal diode will be about 0.3V. At very low diode currents of around 1µA the drop will be much lower, typically about 0.1V.

This is not too much of a problem at higher power levels because an error of a fraction of a volt is quite a small percentage of a total peak voltage of several tens of volts. We can choose to ignore it or partially compensate by adding a fixed offset to the measured value. About O.6V for a silicon diode or O.3V for a Schottky signal diode such as 1N5711 or BAT 43 is close enough to be reasonably accurate. However, at very low power levels, the voltage drop is a significant fraction of the peak voltage and will lead to increasing errors as the peak voltage is reduced. For example, if the peak voltage is 500mV (+4dBm, or 2.5mW), a voltage drop of 0.2V across the detector diode would result in a measured peak voltage of just 300mV (0.46dBm, or 0.9mW). This problem gets even worse when the peak voltage input approaches 0.1-0.2V and the detector output voltage is close to zero.

 

There are a number of ways to improve the accuracy of a diode peak voltage detector. We could calibrate the meter by hand to eliminate errors at the lower end of the scale. This approach works well in practice but it is time consuming and requires unique calibration curves for individual diodes.

We could apply a small amount of forward bias to the diode which would reduce the voltage drop for RF signals or we could use a second identical diode as a reference to show us the required offset for a given level of current and diode temperature. It would be possible to apply all three methods to obtain the best possible accuracy but to keep things simple; I will adopt only the last method. Figure 3 shows how an opamp and a second diode can be arranged to compensate for the voltage drop of the detector diode. This circuit is due to KI6WX [2]. When used with a closely matched pair of 1N5711 diodes, this circuit will accurately track the input voltage down to a level of well below 0.1 V (-10dBm, or 100µW). If the circuit is to be used with a single-ended power supply, the opamp input and output voltage range must go all the way down to the negative supply rail. I used one half of an LM358. A CMOS input type like the CA3140 would be capable of even better performance.

Homemade HF Antenna Balun

 

A balun is a device that is used at the feed point of a balanced antenna when an unbalanced feed line is desired to feed the antenna. Balun is a contraction for BALanced to UNbalanced. A common example of where a balun would be desired is at the feed point of a dipole antenna when a coaxial transmission line is used. If a balun is not used it is possible for common mode currents to be present on the feed line. The effect of this could be undesirable if the directional properties of the balanced antenna are to be maintained.

Since the feed line usually leads into the shack RF could be present in the shack to create RFI as well as the possibility of receiving excessive amounts of RFI from indoor noise sources. It is often found that a balun is not necessary and everything works just fine feeding the balanced antenna directly with coax cable. When this is possible it may be found that the feed line is an odd multiple of 1/4 wavelength. In this case the transmitter end of the feed line is usually grounded and up from this point on the coax 1/4 wavelength or a multiple thereof will appear as a high impedance. When this high impedance point occurs at the feed point chances of common mode currents are low. Rather then take any chances it is often recommended to use a balun.

There are several different kinds of baluns. Some provide a 1:1 impedance ratio while others can provide 1:1.5, 1:4, and many other impedance ratios. A 1:4 ratio balun would come in handy if you were feeding a folded dipole (200 Ohms) with 50 Ohms coax. For a 1:1 ratio a balun can be constructed using the feed line itself by simply winding about five turns of the feed line around a 2" diameter piece of PVC. I preferred a 1:1 ratio balun that I could easily move from one antenna to another by simply unscrewing the coax.

My balun uses AWG 12 enameled wire trifilar wound on a 6" X 1/2" piece of ferrite rod. 7 turns are tightly wound around the electrical tape covered rod. The free ends of the windings are connected as shown below in the schematic. The whole balun is installed in a 10" piece of 1-1/2" schedule 40 PVC pipe. A SO-239 coaxial connector is installed in the bottom end cap with #4 stainless steel hardware. An eyebolt is installed in the top end cap. The antenna post consist of #10 stainless steel hardware mounted on opposite sides near the top of the PVC pipe.

First I drilled all of the necessary holes, including a drain hole in the bottom end cap, and then painted all of the PVC pieces with olive drab paint the protect from the elements. Next the balun was connected to the SO-239 connector and then the pipe was slid over the balun and cemented in place with PVC cement. At this point the balun was connected to the antenna binding posts. Then the top end cap was installed with PVC cement. I tested the balun by attaching a 50 Ohms termination to the antenna posts and my MFJ-259B via coax to the coax connector on the bottom. The 50 Ohms resistive impedance was reflected back through the balun with little reactance throughout the HF spectrum. Since the design was based upon a tried and true design I am confident that it performs as expected as far as choking off currents.

I found this balun really easy to build and should easily handle a large amount of RF power as long as the SWR of the antenna remains low. A purchased balun may only cost a little more then my homemade version but I had the parts on hand and it was fun to build.

 

HF POWER AMPLIFIER

 

 

In my prototype I used IRF840 in the final. Most of the power FET are designed for high voltage operation. At lower operating voltages they saturates quickly limiting the output power. I had given 120 V for IRF840 it takes 1 Amp at peak. Gate voltage is fixed at 1V. Heavy head sink is essential for IRF. My heat sink measures 30 cm * 6.5 cm. Use mica insulator and heat sink compound for fixing IRF.

You can directly replace IRF840 with many of the power FET like IRF830, IRF530, IRF540 etc... When using a different IRF, supply voltage should be changed to less than half the maximum drain voltage (Vds). A zener diode rated slightly higher than the twice the supply voltage connected across drain and source can prevent drain source breakdown. Peak to peak gate voltage of magnitude more than 20 Volts can destroy the FET instantaneously. Two numbers of 15 Volt zener diodes are used to keep gate voltage swing below 20 Volts. Specifications for some of IRF series are given below.